Permanent magnet and process for producing the same



Patented June 25, 1940 PERMANENT MAGNET AND PROCESS FOR PRODUCING THE SAME Giinter Wassermann, Frankfort-on-the-Main,

Germany, asslgnor to American Lurgi Corporaon New York, N. Y., a corporation of New No Drawing. Application November 26, 1938, Se-

rial No. 242,636. In Germany November 26,

4 Claims.

The invention relates to permanent magnets and to a process for producing the same.

It is well known that permanent magnets may be made from various metals and metal alloys 5 having magnetic characteristics. One type of alloy frequently used for this purpose contains iron, nickel and aluminum. Magnets formed from suchalloys are generally produced by casting, since it is difficult to work the magnetic materials because of their great hardness. Such cast magnets have a coarse crystalline structure and are very brittle. Their resistance to mechanical blows, or to centrifugal force where they are used in rotating machines, is very low so that they are not practical for such purposes. Efi'orts have been made to produce magnets having greater mechanical resistance from such alloys by binding together powdered particles of the magnetic alloys with a binding agent having no ferro g0 magnetic properties. Ingots of the alloys have been broken up, and the powder thus obtained pressed together in the presence of a binding agent. This binding agent, however, deleteriously affects the magnetic properties of the alloys,

5 and renders the resulting articles of very low magnetic strength.

Effort has also been made to produce alloys by sintering. The powder is molded in a press under a high pressure and heated to a high sintering temperature. However, the magnets thus obtained also have low magnetic values as compared with the cast alloys, even though mechanically they are stronger. The value of the remanence is particularly low, and such magnets are practically useless.

The present invention relates to the production of iron-nickel-aluminum alloys having high magnetic properties and great mechanical strength by a sintering process. According to the invention, a mixture of powders of the different in-' gredients of the alloy is not merely pressed and subjected to a sintering temperature, but is first preheated to a lower temperature, again powdered, and then compressed and sintered. I have found that by this procedure an alloy of great strengthwhich retains its magneto qualities may be produced.

According to the invention, the three metals in the form of a powder are intimately mixed. The preheating is then carried out at a temperature higher than the melting point of the aluminum, but lower than that at which complete sintering of the different metals takes place. Preferably the heating is within the range of 650 C. to 900 C. Theperiod for which the heating takes place may be relatively short, as, for instance, from thirty minutes to one hour. The preheating is preferably carried out under non-oxidizing conditions, as for instance in a vacuum, or in an atmosphere of an inert gas or a reducing gas such 5 as hydrogen. This preheating bakes the mixture together lightly by the melting of the aluminum. Preferably the mixture is then reconverted into powder form by regrinding. This pretreated powder is then subjected to a pressure as high 10 as possible and then sintered at temperatures betwen 1200 C. and the fusing point of the mixture, preferably at 1300 C. during several hours.

The resulting product has a high mechanical strength, and at the same time has high magnetic 15 qualities comparable to those of the cast alloys. Furthermore, there is no increase in volume during sintering as occurs when the metals have not been preheated according to the invention.

According to a preferred form of the invention, 30 the size of the grains of the iron in the powder which is treated by this process is of importance, although this grain size is not a necessary feature of the invention. As disclosed in my copending application Serial No. 242,637 executed of even 35 date herewith, the iron particles should be of such dimensions that at least a great majority of them will pass through a 250 screen. Preferablyatleast of the iron present is in the condition of such fine particles, although the balance may 30 contain particles as large as those which would pass through a 145 screen.

Within the scope of the invention, it is not necessary that all three metals be subjected to the preheating treatment. It is sufficient to pre- 35 heat the aluminum and one of the other two metals, the third metal being added as a powder to the reground powder resulting from the preheating treatment.

The invention is applicable to iron-nickel- 40 aluminum alloys of magnetic character in general, that is, to alloys composed essentially of these three ingredients. It is particularly applicable to alloys either composed substantially entirely of iron, nickel and aluminum, or to such 45 alloys which contain small or moderate amounts of other metals, for instance of cobalt and/or titanium.

There are given hereafter some examples of methods of carrying out the invention. 50

Example 1 Powdered iron, nickel and aluminum are mixed together. The mixture contains of iron, 22% of nickel and 13% of aluminum. This mix- 55 ture is then heated for one-half hour at 700 C. in a hydrogen atmosphere. After the heating is completed, the product is reground.

This reground powder is subjected to a high pressure and then heated to a temperature of 1,250 C. for several hours. The resulting mass has a high mechanical strength and high magnetic properties.

Example 2 The iron and aluminum powder of Example 2 are mixed and subjected to the preheating treatment of Example 2. After regrinding, the nickel powder is mixed with the iron-aluminum mixture, and the resulting product is sintered in the manner described for Example 2.

Within the scope of the invention, the nickel and aluminum powder may be preheated in the manner described in Example 3 and the iron powder added thereto after regrinding.

While I have described herein some embodiments of my invention I wish it to be understood that I do not intend to limit myself thereby except within the scope of the appended claims.

I claim:

1. A process of producing a permanent magnet which comprises sintering a pressed powder containing a mixture of iron, nickel and aluminum in proportions to produce a magnetic ma- C. for thirty minutes to one hour, grinding the resulting product, and pressing and sintering the ground mix ture between 1200 C. and the fusing point of -the mixture.

3. A process of producing permanent magnets of iron-nickel-aluminum alloys having magnetic characteristics, which comprises mixing the aluminum and one of the other metals in the form of powder and heating the mixture at about 650 C. to 900 C. for thirty minutes to one hour, grinding the resulting product, adding the third metal in the form of a powder, and subjecting the mixture of the three metals under high pressures to a sintering temperature of between about 1200 C. and the fusing point of the mixture.

4. A permanent magnet formed by sintering a pressed powder, containing a mixture of iron, nickel and aluminum in proportions to produce a magnetic material, at a temperature between about 1200 C. and the fusing point of the mixture, in which powder the aluminum and at least one of the other metals have previously been mixed and subjected to a heat treatment in powder form at about 650 C. to 900 C. for thirty minutes to one hour, and the resulting product again powdered by grinding.

GI'JNTER WASSERMANN. 

